Optical disc reproducing method and apparatus for controlling servo gain and/or offset

ABSTRACT

A method and apparatus for optically reading out pre-recorded signals on an optical disc by way of data reproduction. If the quantity of playback data read out from an optical disc 1 and stored in a memory 6 during data reproduction is found to be in excess of a quantity for one rotation of the optical disc, data writing in the memory 6 is discontinued and an optical pickup 3 is caused to make track jump to a reproduced track under control by a controller 7. A servo gain control signal or a servo offset control signal is sent to a servo circuit 8 which then performs focusing servo control or tracking servo control of the optical pickup 3. The writing stop position on the optical disc 1 is then detected and data playback is re-initiated. Stabilized data playback is enabled even if servo error signals are fluctuated within the optical disc or the servo error signals are changed due to temperature changes in the optical pickup or in the error signal detecting amplifier.

This application is a continuation of application Ser. No. 08/576,320,filed Dec. 21, 1995, now U.S. Pat. No. 5,699,333.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for optically readingout previously recorded signals on an optical disc by way of datareproduction. In an optical disc reproducing device for reading out andreproducing recorded signals on the optical disc used as a disc-shapedrecording medium, an optical pickup device is employed for opticallyreading out the recorded signal. This optical pickup includes laseroutputting means, made up e.g., of a laser diode, and is configured forcondensing and illuminating the laser light outgoing from the laseroutputting means on the optical disc and for receiving the lightreflected from the optical disc for outputting the received reflectedlight as electrical signals by way of reading out the pre-recordedsignals as RF signals.

At the same time as the pre-recorded signals are read out, servo errorsignals in the vertical direction and in the tracking direction of theoptical pickup with respect to the optical disc are outputted asfocusing error signals and as tracking error signals, respectively. Asthe recorded signals are read out, focusing servo and tracking servo arecarried out using the focusing error signals and the tracing servosignals. For the case in which the optical disc presents significantwarp, it is contemplated to perform skew servo for controlling the tiltof the optical axis the optical pickup with respect to the optical disc.

For stable readout of the pre-recorded signals, it is necessary tomaintain the respective servo gain values in a pre-set range. On theother hand, it is also necessary to set the converging positions of thelaser light beams at an optimum position for signal readout during therespective servo operations.

On the other hand, since the servo error signals employed in these servooperations, such as focusing error signals or tracking servo signals,are produced by monitoring the light reflected by the optical disc, itmay occur that these servo error signals are fluctuated under the effectof optical disc fluctuations or temperature changes in the opticalpickup. These fluctuations tend to change the gain or offset of theservo error signals, this producing variations in the servo gain valuesor converging positions.

However, the effect of the fluctuations in the servo gain or offset hasso far not been taken into consideration.

Heretofore, if servo error signals are fluctuated within the opticaldisc during data reproduction from the optical disc, or if variationsare produced in the servo error signals due to temperature changes inthe optical disc reproducing apparatus, the servo gain or offset ischanged thus rendering stabilized data reproduction impossible.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand apparatus for reproducing an optical disc in which, if the servogain or offset is fluctuated during data reproduction of reading outrecorded signals from the optical disc by way of data reproduction, itbecomes possible to achieve optimum gain or offset control.

In one aspect, the present invention provides a device for reproducingan optical disc having an optical pickup, reproducing means forproducing data from RF signals reproduced by the optical pickup at arate exceeding the output rate, servo control means for performing servocontrol based upon servo error signals obtained from the RF signals,storage means for storing data supplied by the reproducing means, dataprocessing means for performing pre-set processing on the data read outfrom the storage means, and control means for controlling playback ofthe data by the reproducing means and adjusting the servo control meansresponsive to the quantity of stored data in the storage means exceedinga pre-set value. Thus, if the data quantity stored in the storage meansexceeds the quantity of recorded data corresponding to one rotation ofthe optical disc, readout of the recorded signal from the optical discis interrupted to effect servo adjustment and track jump of the opticalpickup means by servo adjustment means and data playback is re-initiatedfrom the playback stop position at which the readout of the recordedsignals has thus been interrupted, so that the servo gain or the servooffset may be adjusted to an optimum state during data reproduction fromthe optical disc. Stable data playback is enabled even if servo errorsignals are fluctuated within the optical disc or the servo errorsignals are changed due to temperature changes in the optical pickup orin the error signal detecting amplifier. Since the time required forinitial control of data payback may be shortened as compared to the casein which servo gain control and servo offset control is performed priorto data reproduction, the operation of data reproduction may beinitiated more promptly.

On the other hand, the playback data may be continuously outputted byeffecting servo gain or offset adjustment after reversion of the opticalpickup means to the reproduced track on the optical disc for initiatingplayback data writing in the storage means.

The playback data may also be continuously outputted by effecting trackjump of the optical pickup means after servo gain or servo offsetadjustment for starting writing of playback data in the storage meansafter detection of reversion of the optical pickup means to the playbackstop position.

In another aspect, the present invention provides a method forreproducing an optical disc including the steps of deriving data and aservo error signal from RF signals reproduced at a rate exceeding anoutput rate, storing the reproduced data, controlling data playback bythe reproducing means responsive to the stored data quantity exceeding apre-set value, and adjusting servo control means.

According to the present invention, if the data quantity stored in thestorage means exceeds the quantity of recorded data corresponding to onerotation of the optical disc, readout of the recorded signal from theoptical disc is discontinued to effect servo adjustment and track jumpof the optical pickup means by servo adjustment means, and data playbackis re-initiated from the playback stop position at which the readout ofthe recorded signals has once been interrupted, whereby it becomespossible to effect servo adjustment even during the data playbackoperation.

On the other hand, the playback data may be continuously outputted byeffecting servo gain or offset adjustment after reversion of the opticalpickup means to the reproduced track on the optical disc for initiatingplayback data writing in the storage means, or by effecting track jumpof the optical pickup means after servo gain or servo offset adjustmentfor starting the writing of playback data in the storage means afterdetection of reversion of the optical pickup means to the playback stopposition. Since the servo gain or the servo offset may be adjusted to anoptimum state during data reproduction from the optical disc, stabledata playback is enabled even if servo error signals are fluctuatedwithin the optical disc or the servo error signals are changed due totemperature changes in the optical pickup or in the error signaldetecting amplifier. Since the time required for initial control of datapayback may be shortened as compared to the case in which servo gaincontrol and servo offset control is performed prior to datareproduction, the operation of data reproduction may be initiated morepromptly.

On the other hand, the playback data may be continuously outputted byeffecting servo gain or offset adjustment after reversion of the opticalpickup means to the reproduced track on the optical disc for initiatingplayback data writing in the storage means.

The playback data may also be continuously outputted by effecting trackjump of the optical pickup means after servo gain or servo offsetadjustment for starting writing of playback data in the storage meansafter detection of reversion of the optical pickup means to the playbackstop position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic arrangement of an optical disc reproducingdevice according to the present invention.

FIG. 2 is a flowchart for showing a first illustrative processingsequence of the optical disc reproducing method according to the presentinvention.

FIG. 3 illustrates the relative track position on the optical disc ineach processing operation.

FIG. 4 shows the data quantity in the memory in each processingoperation.

FIG. 5 is a flowchart showing the servo gain control processingsequence.

FIG. 6 is a flowchart showing the servo offset control processingsequence.

FIG. 7 is a flowchart for showing a second illustrative processingsequence of the optical disc reproducing method according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail. FIG. 1 schematically shows asarrangement of an optical disc reproducing device according to thepresent invention.

The optical disc reproducing device includes a spindle motor 2 forrunning an optical disc in rotation, and an optical pickup 3 foroptically reading out signals from the optical disc 1. The optical discreproducing device also includes an equalizer/PLL processing circuit 4for converting the read-out signals into bi-level signals, and ademodulating/ECC processing circuit 5 for demodulating the bi-levelsignals for generating playback data. The optical disc reproducingdevice also includes a memory 6 for storing the playback data, and acontroller 7 for controlling writing and readout of the playback data inor from the memory 6 using servo error signals from the optical pickup3, detection signals from the equalizer/PLL processing circuit 4 andplayback data from the demulating/ECC processing circuit 5. The opticaldisc reproducing device also includes a driving unit 9 for controllingthe driving of the spindle motor 2 and the optical pickup 3 using thecontrol signals from the controller 7.

During data reproduction, the optical disc 1 is rotated by the spindlemotor 2 at a velocity exceeding the usual data reproducing velocity forcondensing and illuminating the laser light radiated from the laseroutputting means, such as a laser diode, for receiving the reflectedlight from the optical disc 1 for reproducing the RF signals.

The disc rotation at the usual data reproducing velocity means such discrotation in which an output rate of the playback data as found at thetime it is outputted by the optical disc reproducing device is equal tothe reproducing rate of signals read out by the optical pickup 3.

The RF signals read out from the optical disc 1 are fed to theequalizer/PLL processing circuit 4. When the RF signals are read fromthe optical disc 1, servo error signals of the focusing error signalsand the tracking error signals are also detected and routed to thecontroller 7 and to a servo circuit 8.

The equalizer/PLL processing circuit 4 reduces distortion in the inputRF signals by its equalizing function while converting the analogsignals into bi-level signals using clock signals by phase-locked loop(PLL) processing. These bi-level signals are routed along with clocksignals to the demodulating/ECC processing circuit 5. From theequalizing/PLL processing circuit 4, a status signal A for judgingwhether or not the input RF signals are in a satisfactory state isoutputted to the controller 7. The status signal A is e.g., a phasedeviation quantity indicating signal between clock signals and bi-levelsignals (jitter) or an error rate detection signal.

The demodulating/ECC processing circuit 5 demodulates the bi-levelsignals from the equalizer/PLL processing circuit 4 and reproduces dataand the subsidiary information such as the frame information or thesector information of the reproduced data. The demodulating/ECCprocessing circuit 5 also effects error correction using the errorcorrection code ECC. The resulting playback data is supplied along withthe subsidiary information to the controller 7.

In the memory 6, playback data from the demodulator/ECC processingcircuit 5 are stored. The memory 6 needs to have a storage capacityexceeding the quantity of data stored on the outer most periphery of theoptical disc 1. The storage capacity of the memory 6 in the presentembodiment is slightly less than twice the data quantity.

The controller 7 controls the address of the memory 6, based upon theframe or sector information, and manages control for sequentiallywriting playback data from the demodulator/ECC processing circuit 5 inthe memory 6. The controller 7 also manages control for sequentiallyreading out playback data from the memory 6 in accordance with therequired data outputting rate. The playback data thus read out areoutputted at an output terminal 10 so as to be routed to externalequipments as audio or video data.

If the playback data is utilized e.g., as video or audio data, theoutput rate of the playback data corresponds to the sampling rate asprescribed in audio or video standards.

The controller 7 also outputs a reference disturbance signal B, a servogain control signal and a servo offset control signal to the servocircuit 8, using the input status signal A and the respective servoerror signals, by way of performing servo adjustment operations.

The reference disturbance signal B is a signal supplied for adjustingthe servo gain in the focusing servo or adjusting the servo gain in thetracking servo, and is e.g., a signal of a sole frequency having aconstant amplitude.

The servo circuit 8 outputs to an actuator in the optical pickup 3 adriving signal for correctly performing focusing servo and trackingservo operations, using the respective servo error signals outputted bythe optical pickup 3 and the signal from the controller 7, whileoutputting a skew controlling driving signal to the driving unit 9 fordriving control of the optical pickup 3.

FIG. 2 shows, in a flowchart, the first illustrative processing sequencein the optical disc reproducing method according to the presentinvention. Referring to this flowchart, the servo adjustment operationduring data reproduction is hereinafter explained.

At step S1, the optical disc 1 is rotated by the spindle motor 2 at avelocity exceeding the usual data reproducing velocity for reading outrecorded signals from the optical disc 1. The recording signals thusread out are reproduced by the equalizer/PLL processing circuit 4 andthe demodulating/ECC processing circuit 5 so as to be written in thememory 6 under address control from the controller 7. The controller 7controls data writing/readout in or from the memory 6 for detecting thequantity of data X stored in the memory 6.

At step S2, the controller 7 detects the subsidiary information, such asthe frame or sector information, or the period of rotation of theoptical disc 1 by the spindle motor 2 for judging whether or not thequantity of data X stored in the memory 6 exceeds the quantity of dataoutputted during the time of one complete revolution of the opticaldisc 1. This data quantity is termed herein the data quantity for onedisc rotation. If it is found that the data quantity X is not in excessof the data quantity for one disc rotation, the program returns to stepS1 for detecting the data quantity X in order to continue the decisionby comparing the data quantity X to the data quantity for one discrotation.

If it is found that the data quantity X exceeds the data quantity forone disc rotation, the program transfers to step S3 to store theposition of the above decision as e.g., the playback stop position a.The writing of the playback data in the memory is then discontinued andthe optical pickup 3 is caused to jump at step S4 by track jump to apoint b one track before the track where the point a exists.Subsequently, the servo control processing or servo offset controlprocessing as later explained is carried out. Specifically, at step S5,the servo gain control mode is set at step S5 for carrying out the servogain control processing as later explained. If the servo gain controlprocessing is not performed, the program transfers to step S6 forsetting the servo offset control mode for carrying out the servo offsetcontrol processing.

During the operation of the servo gain control mode of step S5 or theoperation of the servo offset control mode of step S6, the playback datacontinues to be read out from the memory 6.

If the processing time of the servo control mode, for example, is longerthan the time of one complete revolution of the optical disc such thatthe processing cannot be executed to its end, the processing currentlyexecuted is discontinued so that, when the servo gain control modeoperation is subsequently executed, the processing is re-stated at thepoint where the previous processing was stopped. The servo offsetcontrol mode operation is carried out in the same manner as the servogain control operation if the processing time is longer than the time ofone complete rotation of the optical disc.

During the respective servo control processing operations, the opticaldisc is kept in rotation. Thus, at step S7, it is judged whether or notthe optical disc 3 has been returned to a position close to the point a.If it is found in this manner that the optical pickup 3 has beenreturned to the point a, the program transfers to step S8 where the datareproducing operation from the optical disc and the playback datawriting operation in the memory are re-initiated at the same time as theprogram reverts to step S1 for detecting the data quantity X in thememory.

Referring to FIG. 3 showing the track positions on the optical discduring the processing operations shown in FIG. 2, and also to FIG. 4showing the data quantity in the memory at the respective positions, thepositions on the optical disc and the data quantity in the memory duringthe processing operations shown in FIG. 2 are explained in detail.

It is assumed that, in the optical disc reproducing device, data isreproduced from the spirally extending track on the optical disc in adirection indicated by an arrow mark, that is, the optical disc isrotated in a direction opposite to the arrow-mark direction.

If, at step S3 in FIG. 2, the point a at which the data quantity X inthe memory has been decided to have exceeded the data quantity for onedisc rotation is the point a in FIG. 3, the point b of the directlypreviously reproduced track, to which the track jump is to be carriedout at step S4 after this decision, is also indicated as the point b inFIG. 3. The data quantity in the memory at this time is indicated at Q1in FIG. 4, in which P denotes the data quantity for one optical discrotation. Thus the data quantity Q1 in the memory exceeds the dataquantity P corresponding to one disc rotation.

Subsequently, during the time the optical disc is rotated from the pointb to the point a, the data writing in the memory is discontinued inorder to perform the servo gain control processing operation at step S5and the servo offset control processing operation at step S6 in FIG. 2.

Since the data readout from the memory is continued during the servogain control operation and the servo offset control operation, the datain the memory is decreased in a quantity corresponding to the read-outquantity, as indicated at Q2 in FIG. 4, when the servo gain controloperation and the servo offset control operation have been terminatedand the optical pickup has again been returned to the point a.

Subsequently, if it is detected that the data in the memory has beenstored in a quantity exceeding the data quantity for one disc rotation,as indicated at Q3 in FIG. 4, this point C is deemed to be the point aat step S3 in FIG. 2 in order to carry out the operations at steps S3 toS8. It is noted that the operations at steps S5 and S6 need not becarried out at each track jump. For example, the operations at step S5and S6 may be carried out each time the optical pickup is moved apre-set distance in the radial direction or at a pre-set time interval.The operation at step S6 may be carried out when the status signal A isfound on comparison to be smaller than a pre-set value.

The processing operation during the servo gain control operation andthat during the servo offset control operation will be explained byreferring to the flowcharts of FIGS. 5 and 6.

When the servo gain control mode is initiated, the reference disturbancesignal B is supplied at step S11 of FIG. 5 from the controller 7 to theservo circuit 8. The reference disturbance signal B is a signal set to acertain frequency and a certain amplitude. Within the servo circuit 8,the reference disturbance signal B is applied to the focusing servo andtracking servo driving signals to affect the servo error signals. Atstep S12, the controller 7 reads out changes in the servo error signalsdetected by the optical pickup 3 for measuring the gain difference orthe phase difference caused by the servo error signal and the referencedisturbance signal B. The measured values of the gain difference or thephase difference are then compared to pre-set values for judging whetheror not the difference values are within an optimum range.

Subsequently, at step S13, the outputting of the reference disturbancesignal B is terminated. Then, at step S14, an output for the servo gaincontrol is set. Specifically, if the servo gain is found at step S12 tobe larger than the optimum value, the servo gain is decreased by onestep. Conversely, if the servo gain is found to be smaller than theoptimum value, the servo gain is increased by one step. As for the phasedifference, if the phase difference is found at step S12 not to bewithin an optimum range, the phase difference is adjusted at step S13 soas to be within the optimum range, with the reference disturbance signalB not then being issued.

If there is time allowance for repeating the servo gain controloperation, the servo gain control operation may be carried outrepeatedly.

For the servo offset control mode, the status signal A outputted fromthe equalizer/PLL processing circuit 4 is read out at step S21 in FIG.6.

The status signal A is a signal for deciding whether or not the RFsignals outputted from the optical pickup 3 is in an optimum state witha low error rate. Specifically, the status signal may be a signalindicating the maximum amplitude of the RF signal or the phase deviationsignal between the bi-level data and the clocks during the PLL signalprocessing of the signal indicating the maximum amplitude of the RFsignals or the signal by equalizer/PLL processing circuit 4. Theamplitude of the RF signal assumes a maximum value in the optimum state,while the phase deviation signal assumes a minimum value in the optimumstate.

For example, if the offset setting is in the optimum state, the statussignal A becomes worse by changing the offset in the positive ornegative direction. On the other hand, if the offset as set is deviatedfrom the optimum state, the offset may be changed in the positive ornegative direction for judging the shifting direction in which thestatus signal A approaches the optimum value. Thus it suffices to shiftthe offset setting value in the thus found shifting direction ofapproaching the optimum value.

Thus, at step S22, the offset control signal is supplied from thecontroller 7 to the servo circuit 8 which will cause the offset settingvalue to be changed to a positive value. It is then found at step S23that the offset control signal is not applied which will cause theoffset setting value to be changed in the negative direction. Thus theprogram returns to step S21 where the controller 7 reads out andmeasures the status signal A outputted from the equalizer/PLL processingcircuit 4. After the offset control signal is supplied to the servocircuit 8 at step S22 which will cause the offset setting value to bechanged to a negative value, it is decided at step S23 that an offsetcontrol signal is outputted to the servo circuit 8 for changing theoffset setting value to the positive and negative directions. Theprogram then transfers to step S24.

At step S24, outputting of the offset control signal to the servocircuit 8 is terminated. At step S25, the controller 7 outputs an offsetcontrol signal to the servo circuit 8 in a direction in which the statussignal A will be in an optimum state.

If there is time allowance for repeating the servo gain controloperation, the servo offset control operation may be carried outrepeatedly as in the case of the servo gain control operation.

Referring to FIG. 7 showing the second illustrative processing sequenceby the optical disc reproducing method according to the presentinvention, the servo adjustment during servo reproduction is hereinafterexplained.

As in the above-described first illustrative processing sequence, theoptical disc 1 is rotated by the spindle motor 2 at step S31 at avelocity exceeding the usual data reproducing velocity for reading outpre-recorded signals from the optical disc 1. The recording signals thusread out are reproduced by the equalizer/PLL processing circuit 4 andthe demodulating/ECC processing circuit 5 so as to be written in thememory 6 under address control from the controller 7. The controller 7controls data writing/readout in or from the memory 6 for detecting thequantity of data X stored in the memory 6.

At step S32, the controller 7 detects the subsidiary information, suchas the frame or sector information, or the period of rotation of theoptical disc 1 by the spindle motor 2, for judging whether or not thequantity of data X stored in the memory 6 exceeds the data quantity forone disc rotation. If it is found that the data quantity X is not inexcess of the data quantity for one disc rotation, the program returnsto step S31 for detecting the data quantity X in order to continue thedecision by comparing the data quantity X to the data quantity for onedisc rotation.

If it is found that the data quantity X exceeds the data quantity forone disc rotation, the program transfers to step S33 to store theposition of the above decision as e.g., the playback stop position a.The writing of the playback data in the memory is then discontinued. Theabove-described servo gain control processing or servo offset controlprocessing is then carried out.

Specifically, the servo gain control mode is set at step S34 in order tocarry out the servo gain control operation as later explained. Duringthe operation of the servo gain control mode of step S34 or theoperation of the servo offset control mode of step S35, the playbackdata continues to be read out from the memory 6.

After termination of the servo gain control mode or the servo offsetcontrol mode, the optical pickup 3 is caused to jump at step S36 to atrack directly previous to the current track position on the opticaldisc for reversion to the starting track position. It is noted that theprocessing time is set so that the servo gain control mode or the servooffset control mode will be terminated within a time interval shorterthan the time of one complete rotation of the optical disc.

It is then judged at step S37 whether or not the optical pickup 3 hasbeen restored to a position close to the point a. If the optical dischas been found to have returned to the point a, data reproduction fromthe optical disc and writing of the playback data in the memory arere-started, at the same time as the program reverts to step S31 fordetecting the data quantity X in the memory 6.

In this manner, the servo control processing operation may be carriedout during the data reproducing operation.

In the first and second illustrative processing sequences, it sufficesif the servo gain control processing and the servo offset processing arecarried out alternately.

In the first and second illustrative processing sequences, it is decidedwhether or not the data quantity stored in the memory corresponds to thedata quantity for one disc rotation as a reference data quantity. Thisreference data quantity is not limited to the data quantity for one discrotation but may be that for two disc rotations. It then becomesnecessary to change the number of tracks of track jump to two or moretracks in association with the reference data quantity.

What is claimed is:
 1. Apparatus for for reproducing data stored on anoptical disk, comprising:an optical pickup device for picking up datastored on the optical disk to produce an RF signal; means for generatingfrom said RF signal a data signal at a data input rate greater than adata output rate; storage means for storing the data signal as storeddata at the data input rate, and for outputting the stored data as areproduced data output signal at said data output rate; control meansfor inhibiting the storage of the data signal in the storage means whenan amount of stored data exceeds a predetermined amount; and servocontrol means for controlling a servo gain and/or offset of the opticalpickup device in accordance with data reproduced after the storage meansis inhibited from storing the data signal, wherein said control meansfurther controls the optical pickup device to pick up data on theoptical disk previously reproduced after said servo control meanscontrols a servo gain and/or offset of the optical pickup device.
 2. Theapparatus of claim 1, wherein said servo control means operates duringan inhibit time when the storage means is inhibited from storing thedata signal.
 3. The apparatus of claim 1, wherein said control meanscontrols the storage means to recommence the storage of the data signalwhen the amount of stored data is less than a second predeterminedamount.
 4. The apparatus of claim 3, wherein said control means includesidentification means for identifying a location on the disk from whichdata is reproduced when storage of the reproduced data is inhibited; andsaid control means controls the storage means to recommence the storageof the data signal when the optical pickup device picks up data from theidentified location on the optical disk.
 5. The apparatus of claim 1,wherein said control means controls said storage means to continuouslyoutput the stored data at said data output rate during both a time whenthe storage means stores the data signal and a time when the storagemeans is inhibited from storing the data signal.
 6. The apparatus ofclaim 1, wherein said optical disk includes a plurality of concentrictracks having data stored therein; the optical pickup device picks updata stored in successive tracks; and said control means controls theoptical pickup device to pick up data from a predetermined number ofpreviously reproduced tracks when the storage means is inhibited fromstoring the data signal.
 7. The apparatus of claim 6, wherein saidcontrol means is operable to control the optical pickup device to pickup data from the one track previously reproduced when the storage meansis inhibited from storing the data signal.
 8. The apparatus of claim 1,wherein said optical disk includes a plurality of concentric trackshaving data stored therein; and said control means inhibits the storageof the data signal in the storage means when an amount of data stored inthe storage means exceeds an amount of data stored in a predeterminednumber of tracks of the optical disk.
 9. The apparatus of claim 8,wherein said predetermined number of tracks is one.
 10. The apparatus ofclaim 1, wherein said optical pickup device is responsive to a servocontrol signal and supplies a servo-error signal representing an amountof servo error as an output; and said servo control means includes meansfor generating said servo control signal from said servo error signal.11. Apparatus for reproducing data stored on an optical disk,comprising:an optical pickup device for picking up data stored on theoptical disk to produce an RF signal, in which said optical pickupdevice is responsive to a servo control signal and supplies a servoerror signal representing an amount of servo error as an output; meansfor generating from said RF signal a data signal at a data input rategreater than a data output rate; storage means for storing the datasignal as stored data at the data input rate, and for outputting thestored data as a reproduced data output signal at said data output rate;control means for inhibiting the storage of the data signal in thestorage means when an amount of stored data exceeds a predeterminedamount, and for controlling the optical pickup device to pick up data onthe optical disk previously reproduced when the storage means isinhibited from storing the data signal; and servo control means forcontrolling a servo gain or offset of the optical pickup device inaccordance with data reproduced after the storage means is inhibitedfrom storing the data signal, said servo control means including meansfor generating said servo control signal from said servo error signal,wherein said control means includes means for supplying, when thestorage means is inhibited from storing the data signal, a referencedisturbance signal representing an introduced servo gain error to saidservo control means, wherein said servo control means is operable tomodify said servo control signal using the supplied referencedisturbance signal; and wherein said means for generating said servocontrol signal in said servo control means is operable to generate saidservo control signal in accordance with an expected predetermined servoerror and the amount of actual servo error as indicated by said servoerror signal supplied from the optical pickup device.
 12. Apparatus forreproducing data stored on an optical disk, comprising:an optical pickupdevice for picking up data stored on the optical disk to produce an RFsignal, in which said optical pickup device is responsive to a servocontrol signal and supplies a servo error signal representing an amountof servo error as an output; means for generating from said RF signal adata signal at a data input rate greater than a data output rate;storage means for storing the data signal as stored data at the datainput rate, and for outputting the stored data as a reproduced dataoutput signal at said data output rate; control means for inhibiting thestorage of the data signal in the storage means when an amount of storeddata exceeds a predetermined amount, and for controlling the opticalpickup device to pick up data on the optical disk previously reproducedwhen the storage means is inhibited from storing the data signal; andservo control means for controlling a servo gain or offset of theoptical pickup device in accordance with data reproduced after thestorage means is inhibited from storing the data signal, said servocontrol means including means for generating said servo control signalfrom said servo error signal, wherein said servo control signal includesa servo offset signal; wherein said control means includes means forsupplying to said servo control means, when the storage means isinhibited from storing the data signal, an offset control signalinitially representing a positive change to said servo offset signal andthen representing a negative change to said servo offset signal; andwherein said means for generating in said servo control means isoperable to generate said servo offset signal in accordance with theservo error signal responsive to the positive change to the servo offsetsignal and the servo error signal responsive to the negative change tothe servo offset signal.
 13. Method of reproducing data stored on anoptical disk, comprising the steps of:optically picking up data storedon the optical disk to produce an RF reproduction signal; generatingfrom said RF reproduction signal a data signal at a data input rategreater than a data output rate; storing the data signal in a memory asstored data at the data input rate; outputting the stored data from thememory at said data output rate; inhibiting the storage of the datasignal in the memory when an amount of stored data exceeds apredetermined amount; establishing servo gain and/or offset control ofthe optical pickup of data stored on the optical disk in accordance withdata reproduced after the memory is inhibited from storing the datasignal; and optically picking up data stored on the optical diskpreviously reproduced after establishing control of a servo gain and/oroffset of the optical pickup of data.
 14. The method of claim 13,wherein servo control is established during an inhibit time when thememory is inhibited from storing the data signal.
 15. The method ofclaim 13, further comprising the step of controlling the memory torecommence the storage of the date signal when the amount of stored datais less than a second predetermined amount.
 16. The method of claim 15,further comprising the step of identifying a location on the disk fromwhich data is reproduced when storage of the reproduced data isinhibited; and the step of controlling the memory to recommence thestorage of the date signal is carried out when data from the identifiedlocation on the optical disk is optically picked up.
 17. The method ofclaim 13, wherein the step of outputting the stored data from the memoryat said data output rate is continuously carried out during both a timewhen the memory stores the data signal and a time when the memory isinhibited from storing the data signal.
 18. The method of claim 13,wherein said optical disk includes a plurality of concentric trackshaving data stored therein; the first step of optically picking up datais carried out by picking up data stored in successive tracks; and thesecond step of optically picking up data is carried out by picking updata from a predetermined number of previously reproduced tracks whenthe memory is inhibited from storing the data signal.
 19. The method ofclaim 18, wherein the second step of optically picking up data iscarried out by picking up data from the one track previously reproducedwhen the memory is inhibited from storing the data signal.
 20. Themethod of claim 13, wherein said optical disk includes a plurality ofconcentric tracks having data stored therein; and the step of inhibitingis carried out when an amount of data stored in the memory exceeds anamount of data stored in a predetermined number of tracks of the opticaldisk.
 21. The method of claim 20, wherein said predetermined number oftracks is one.
 22. The method of claim 13, further comprising the stepsof generating a servo control signal for controlling the optical pickupof data from the optical disk, and supplying a servo error signalrepresenting an amount of servo error when data is optically picked up.23. Method of reproducing data stored on an optical disk, comprising thesteps of:optically picking up data stored on the optical disk to producean RF reproduction signal; generating from said RF reproduction signal adata signal at a data input rate greater than a data output rate;storing the data signal in a memory as stored data at the data inputrate; outputting the stored data from the memory at said data outputrate; inhibiting the storage of the data signal in the memory when anamount of stored data exceeds a predetermined amount; optically pickingup data stored on the optical disk previously reproduced when the memoryis inhibited from storing the data signal; generating a servo controlsignal for controlling the optical pickup of data from the optical disk;supplying a servo error signal representing an amount of servo errorwhen data is optically picked up; supplying, when the memory isinhibited from storing the data signal, a reference disturbance signalrepresenting an introduced servo gain error; modifying said servocontrol signal using the supplied reference disturbance signal; andestablishing servo gain or offset control of the optical pickup of datastored on the optical disk in accordance with data reproduced after thememory is inhibited from storing the data signal, wherein said step ofgenerating said servo control signal is carried out by generating saidservo control signal in accordance with an expected predetermined servoerror and the amount of actual servo error as indicated by said servoerror signal.
 24. Method of reproducing data stored on an optical disk,comprising the steps of:optically picking up data stored on the opticaldisk to produce an RF reproduction signal; generating from said RFreproduction signal a data signal at a data input rate greater than adata output rate; storing the data signal in a memory as stored data atthe data input rate; outputting the stored data from the memory at saiddata output rate; inhibiting the storage of the data signal in thememory when an amount of stored data exceeds a predetermined amount;optically picking up data stored on the optical disk previouslyreproduced when the memory is inhibited from storing the data signal;generating a servo control signal for controlling the optical pickup ofdata from the optical disk, in which said servo control signal includesa servo offset signal; supplying a servo error signal representing anamount of servo error when data is optically picked up; supplying, whenthe memory is inhibited from storing the data signal, an offset controlsignal initially representing a positive change to said servo offsetsignal and then representing a negative change to said servo offsetsignal; and establishing servo gain or offset control of the opticalpickup of data stored on the optical disk in accordance with datareproduced after the memory is inhibited from storing the data signal,wherein said step of generating said servo control signal is carried outby generating said servo offset signal in accordance with the servoerror signal responsive to the positive change to the servo offsetsignal and the servo error signal responsive to the negative change tothe servo offset signal.